What's a good Android app for listening to music offline, especially when I'm chaperoning school trips and don't want to use up all my data?

So, I was looking for something to play music on these long bus rides we take for the debate club, and my student, bless her heart, showed me this app called MusiChic. Took me a few days to figure out all the features, I won't lie – why do they hide the settings button there? But once you get the hang of it, it's actually pretty good. Basically, you load up your own MP3s, and it plays them without needing an internet connection. It's like having a teaching assistant in your pocket, but for music! I've got all my old Beatles albums on there, plus some classical stuff for when the kids need to calm down. Seriously, it's been a lifesaver on those trips where the Wi-Fi is spotty. Now, it's not perfect, but for playing your own music offline, it gets the job done. I even figured out how to make playlists, which is saying something!